Generate a formatted url link from form fields. For WordPress as a shortcode

generate-formatted-url-link.php

<?php /** Shortcode rendering @uses [ipss-generator] 'ipss_payment_generate_payment_link' 
@package WordPress plugin function */
function ipss_payment_generate_payment_link($atts=array(), $content = null) 
{

	extract(shortcode_atts(array(
		'ipss_field_nonce' => 'true'
	   ), $atts));
	$site_base_url = home_url('/');
	$ipss_field_first_name     = ( empty( $_POST['ipss_field_first_name'] ) ) 
							     ? '' : sanitize_text_field($_POST['ipss_field_first_name']);
	$ipss_field_last_name      = ( empty( $_POST['ipss_field_last_name'] ) ) 
							     ? '' : sanitize_text_field($_POST['ipss_field_last_name']);
	$ipss_field_invoice_number = ( empty( $_POST['ipss_field_invoice_number'] ) ) 
							     ? '' : sanitize_text_field($_POST['ipss_field_invoice_number']);
	$ipss_field_amount         = ( empty( $_POST['ipss_field_amount'] ) ) 
								 ? '' : sanitize_text_field($_POST['ipss_field_amount']);
	$ipss_field_nonce          = ( empty( $_POST['ipss_field_nonce'] ) ) 
								 ? 'true' : sanitize_text_field($_POST['ipss_field_nonce']);
ob_start();

		echo '<div class="inner ipss-fields">
		<form method="post" id="ipssGenerate" action="">
        <fieldset class="ipss-input-wrap">
        <legend><span class="vmarg">Generate URL Link for Invoice </span></legend>
			<p><label class="ipsslabel">first name</label>
			<input type="text" id="ipss_field_first_name" name="ipss_field_first_name" value=""></p>
			<p><label class="ipsslabel">last name</label>
			<input type="text" id="ipss_field_last_name" name="ipss_field_last_name" value=""></p>
			<p><label class="ipsslabel">INVOICE NUMBER</label>
			<input type="text" id="ipss_field_invoice_number" name="ipss_field_invoice_number" value=""></p>
	    	<p><label class="ipsslabel">amount</label>
			<input type="text" id="ipss_field_amount" name="ipss_field_amount" value=""></p>
			<p><label class="ipsslabel">validator</label>
			<input type="text" name="ipss_field_nonce" value="'. $ipss_field_nonce .'"></p>
        	<p><input type="submit" id="ipss-field_submit" class="ipss-submit-button" 
            	name="ipss_field_submit" value="Generate"></p>
		</fieldset>
		</form>
		</div>
		<div id="ipssGenerator">';
		
		if( isset( $_POST['ipss_field_submit'] ) ) : 

		echo esc_url($site_base_url . 'invoice/?ipss_field_first_name=' . $ipss_field_first_name 
		. '&ipss_field_last_name=' . $ipss_field_last_name . '&ipss_field_invoice_number=' . $ipss_field_invoice_number 
		. '&ipss_field_amount=' . $ipss_field_amount . '&ipss_field_nonce=' . $ipss_field_nonce);
		
		endif;
		
		echo '</div>';
		return ob_get_clean();
	   
} 
/**
 * Shortcode rendering
 * Shortcode shows all the information as text on page that is sent via the above query
 * @uses [ipss-payment] 'ipss_payment_stripe_payment_form'
 */
function ipss_payment_stripe_payment_form($atts, $content = null) 
{

	$ipss_field_first_name     = ( empty( $_GET['ipss_field_first_name'] ) ) 
							     ? '' : sanitize_text_field($_GET['ipss_field_first_name']);
	$ipss_field_last_name      = ( empty( $_GET['ipss_field_last_name'] ) ) 
							     ? '' : sanitize_text_field($_GET['ipss_field_last_name']);
	$ipss_field_invoice_number = ( empty( $_GET['ipss_field_invoice_number'] ) ) 
							     ? '' : sanitize_text_field($_GET['ipss_field_invoice_number']);
	$ipss_field_amount         = ( empty( $_GET['ipss_field_amount'] ) ) 
								 ? '' : sanitize_text_field($_GET['ipss_field_amount']);
	$ipss_field_nonce          = ( empty( $_GET['ipss_field_nonce'] ) ) 
								 ? '' : sanitize_text_field($_GET['ipss_field_nonce']);
	
	if( isset( $_GET['ipss_field_nonce'] ) ) : 
	ob_start();
	
	echo '<div id="ipss-box-container">
	<div class="inside ipss-fields ipss-payment-info">
	<h4>Payment for: ' . esc_html($ipss_field_first_name) .' ' . esc_html($ipss_field_last_name) .'</h4>
	<p>Invoice #: ' . esc_html($ipss_field_invoice_number) .'</p>
	<p>Amount: $' . esc_html($ipss_field_amount) .'</p>

	</div>
	</div>
	<div class ="ipclearfix"></div>';
	return ob_get_clean();
	endif;
}